1. Technical Field
The invention relates to a projection zoom lens that is mounted on a projection-type display device and that includes six lens groups, four of which are movable, and a projection-type display device mounted with the projection zoom lens. More specifically, the invention relates to a projection zoom lens and a projection-type display device that enlarges and projects luminous fluxes, which carry video information from a light valve of an image display device, onto a screen.
2. Description of the Related Art
In recent years, a projector (projection-type display device) using a light valve such as a liquid crystal display device or a DMD display device has come into wide use. Accordingly, higher advancement is required for an optical system mounted on this projector.
For a projection lens of the above optical system, demanded is a wide angle of view and long back focus that allows an optical member, such as elements or prisms, to be inserted. Also, telecentricity on the reduction side is demanded depending on its usage. With diversification of markets, it is also demanded that the projection lens is made more compact. Moreover, it is demanded to improve the optical performance of the projection lens. From these viewpoints, attention has been paid to the configuration including six lens groups, in which two fixed lens groups are arranged in front of and in rear of four movable lens groups, respectively. For example, JP 2001-350096 A, JP 2003-337283 A, JP 2004-70306 and JP 2005-62226 disclose such a projection lens.
Meanwhile, with development of device technologies, resolution and chromatic aberration correction that meet higher fineness of devices are strongly required. For example, with higher density of pixels of a liquid crystal panel for use in a light valve, a requirement for the optical performance of a projection lens has also been increasingly severe. Specifically, one pixel of the liquid crystal panel is made fine to be about 10 μm, and design capable of substantially reducing various aberrations including chromatic aberration (particularly, lateral chromatic aberration) is demanded.
As liquid crystal panels are made fine, a bright (having a small F number) lens having large aperture is also required so that light that has passed through pixels can reach a screen without losing light intensity, if possible. In addition, in the case where transmissive liquid crystal panels are used as light valves, it is general to combine panels with microlenses together in order to improve illumination efficiency, and increasing the aperture size is very strongly required to the projection lens. Specifically, a bright lens having about 1.6 or less in F number is required.
However, any of the projection lenses disclosed in the above publications is not a projection zoom lens having optical performance capable of responding to pixels on a light valve, having about 10 μm in size.
In particular, since the projection lens disclosed in JP 2005-62226 A has 2.0 in F number and is thus dark, it is difficult to adopt such a projection lens when the transmissive liquid crystal panel is used as a light valve. Since the projection lenses disclosed in JP 2001-350096 A, JP 2003-337283 A and JP 2004-70306 A have a problem in terms of brightness due to its large F number, and besides have a large aberration, it is difficult to adopt any of those projection lenses in the case where liquid crystal to support high density of pixels is used.